1. Field of the Invention
The present invention relates to a liquid ejection head and a liquid ejection apparatus each of which has nozzles from which liquid such as ink can be ejected.
2. Description of the Related Art
A liquid ejection head having an ink supply structure which is able to prevent increase in the viscosity of the ink inside the nozzles is desired.
Japanese Patent Application Publication No. 10-114081 discloses a liquid ejection head comprising: two common ink preparation chambers (common flow channels) which are connected respectively to either side of pressure generating chambers, via ink supply ports; and ink introduction ports via which ink is introduced into the respective ink preparation chambers from the exterior. Of the two ink introduction ports, one ink introduction port is connected to a sub tank, and the other ink introduction port is connected to an ink cartridge, and printing is carried out, while ink is replenished into the sub tank by making the ink pass from the ink cartridge through the liquid ejection head and the ink then flows in reverse by making the ink pass from the sub tank to the ink cartridge through the liquid ejection head.
As shown in FIG. 20, the solvent in the ink evaporates from the meniscus of a nozzle 51 which is not ejecting ink, and hence there is a possibility that the viscosity of the ink increases. If the ink inside the nozzle 51 increases in viscosity, then the ejection speed declines and the image quality deteriorates. If the increase in viscosity increases further, then it becomes impossible to eject ink. If maintenance is carried out in order to remove the ink of increased viscosity by suction, it becomes possible to eject ink again, but in order to carry out maintenance of this kind, in general, it is necessary to halt printing, and therefore the apparatus operating time is reduced and printing costs increase.
Furthermore, in the apparatus described in Japanese Patent Application Publication No. 10-114081, if a pressure differential is applied between the two ink introduction ports which are provided in the ink preparation chamber (common flow chamber), then the flow rates of the ink flowing inside the respective pressure chambers differ. More specifically, a relatively large pressure differential is created on either side of a pressure chamber which is near to the ink introduction port, and a relatively small pressure differential is created on either side of a pressure chamber which is distant from the ink introduction port, and consequently, a relatively large amount of ink flows in a pressure chamber which is near to the ink introduction port, while a relatively small amount of ink flows in a pressure chamber which is distant from the ink introduction port.
If a difference arises in the ink flow rate between the pressure chambers, then not only is there a difference in the gas bubble expulsion properties between the pressure chambers, but furthermore, if the ink flows inside the pressure chamber during printing, then the effect of this ink flow on ejection will vary between the different pressure chambers, and therefore so-called “ejection variations” may arise.
Furthermore, in a liquid ejection head having a so-called matrix structure in which a plurality of nozzles are arranged at high density in order to achieve high image quality, it is difficult to increase the common flow channel in order to circulate the ink, for reasons of space.